The problem started about two weeks ago. The morning of the smithville show I started the 74 and it was hard to keep it running initially. Once it warmed up all was good. On the way to the show, at around 60 mph, the car suddenly felt like the ignition was turned off. The car stumbled a few times and then caught and backfired through the exhaust. On the way home the same thing occurred twice. Yesterday I took it out again. It started fine but on the highway again at around 60 - 70 mph I got the same symptoms. I took it back home and did the following.

Checked plug wires - OK
Checked ignition timing - OK
Checked mechanical advance - OK 10 degrees initial, 34 degrees @ 3000 rpm
Checked vacuum advance = OK
Check carb adjustment = OK and nothing sticking

I took it out again and got the same thing a few times. I started to suspect a bad load of gas so I drove it for an hour or so and got the tank almost empty. I then filled it with premium but only drove it home. Other than a bad load of gas does anyone have any other suggestions? The only thing I can think of is that for some reason I'm not getting juice to the coil intermittently which is causing the engine to misfire and dump a load of gas in the exhaust which is fired when the engine catches again. Does this sound reasonable. If so I'll connect a volt meter to the coil and monitor it when driving to see if I lose voltage. I'm hoping all it was is bad gas.

 

I was going to suggest ignition. Maybe the coil is on its way out or has a loose connection.

 

That's what I thought. Strange though, I can take her through the gears to 4K + each time with no problem. I'm going to have to put a volt meter on the coil and flex the wires. Maybe there's a break somewhere that's intermittent or as you say maybe the coil is going out. The coil is an Accel Super Stock and I doubt that I have 10K miles on it.

 

Same exact thing happened to me (and I made a post about it a few weeks ago). Everyone suggested changing the coil. I haven't done so yet, but that the cheapest & easiest place to start.

D. Ocean
Miami, FLA

 

Bad condeser.... it will cause the problem you describe.

 

No condensor. Electronic conversion. Dwell is dead on throughout rpm range. I'm still thinking it might be wiring related.


Btw. backfires through Dynomax Ultraflows are really really loud.

 

Fuel filter?

 

I think I would drive it more on the new gas and check for water in the gsa tank before going to far with the electronics. Look in the tank and see if you can spot water, I had a water "blob" you could see at the tank bottom and used two bottles of the water out additive. Seem best to try the easiest way out first.

 

opps doubled it

 

I was thinking about fuel also. I have an Edelbrock filter which is solid so I can't see in it to see if it's dirty. I did look in the tank and it appears to be OK but since it's full now may be the time to put a can or two of dry gas in. Maybe I should also replace the fuel filter with a clear one so I won't be wondering about it all the time.

 

I had a similar problems years ago with my 72. It ran good around town and crusing but if I punched it( in the throttle sense it would bog and felt like it would stall. Turns out I had changed the fuel pump prior to this and used regular fuel line from the steel fuel line to the pump. Since these rubber lines weren't the curved "S" hose they kinked under load and shut off gas. When I let the car recover they relaxed and fed enough fuel. As a test at the tiem I used a small hose clamp on the inlet hose to maintain the curve and this solved the problem until I installed the S hose..........10 years later!! Now about punching the car with my fist...nah that's for another post!

Gary

 

Good point. I have the S hoses but I also did a lot of suspension work this past winter. I'll have to make sure there are no kinks in the hose. Thanks.

 

Have you checked the timing chain and gear?

 

my vote goes for fuel related problem.....was the car parked out of your sight where some could have screwed with the gas???

 

I don't think it's the timing chain or gear because the engine was rebuilt less than 5 K miles ago. It's really a nice running engine until it stumbles and backfires. 10 seconds later it's back to being a nice engine. But when it does it's stumbling number you want to pull off the road because it feels like it shut off.

 

I had that happen Years ago with a DD turned out to be the pick-up coil wire broke (HEI) and when the dizzy advanced the wire opened the engine quit dizzy retarded and the wire made conection and the engine started again

Steve

 

I experienced this same problem on my 68 Camaro, turned out that the coil was only running on the secondary circuit, and when power demands came on the electrical system it wouldn't deliver enuf spark, I'm not saying this is your problem juat adding my 0.02

 

Years ago I had a claped out '65 Chevy II with a 283 that would do this whenever I drove it a little too hard. The car originally had a 230 six cylinder and city gearing in it. I put the 283 in it when I was a junior in high school.

One night while chasing an ambulance to the hospital (my wife was in it) I had the little Deuce wound tight out on I 74 going into Cincinnati. All of a sudden she lays down real bad and in the rearveiw merror I see the entire back of the car in flames. Well, I thought, she just shallowed every valve she's got. But then she came right back up. Motor justa singin. Oh well enough of the dramatics.

Turned out to be carbon blowing out of the engine.

I know I could have kept it to one sentance but it was exciting at the time.

BigBlockk

Later.....

 

Did you replace your points to electronics,, like a Pertronics ?? This might be a shot in the dark,, but my car had the same symptoms this spring and finally died in the middle of nowhere. I though the same things as you,, but it was the Ignitor that failed on me..

 

Thanks for all the replies to this thread. It's given me a lot of food for thought. I think this weekend I'll pull the distributor and see if there are any breaks in the wiring that could cause a loss of power. I'll also check the wiring to the coil. For the small investment required I might even change the Pertronix over to a Crane XR1. I kind of like the idea of not having the magnet ring and having a rev limiter. The Pertronix has been in the car for years and has never given me a problem but you never know. A fresh start may be in order. I'm probably also going to change the gas filter to a see-through. I don't like the idea of not being able to see if the filter is contaminated. Again, thanks for all the replies, you guys are great.